Thin film transistor and manufacturing method therefor, array substrate, and display device

ABSTRACT

A thin film transistor and a manufacturing method therefor, an array substrate, and a display device. The thin film transistor includes an active layer, a gate insulating layer, and a gate electrode; the gate insulating layer is located on one side of the active layer; the gate electrode is located on one side of the gate insulating layer distant from the active layer; the gate electrode includes an opening a part of the active layer overlapped with the opening includes a first lightly doped region, a first heavily doped region, and a second lightly doped region that are sequentially arranged along a first direction parallel to a plane where the active layer is located.

TECHNICAL FIELD

Embodiments of the present disclosure relate to a thin film transistor,a manufacturing method thereof, an array substrate and a display device.

BACKGROUND

The thin film transistor (TFT) is a kind of thin film semiconductorelement, which is widely used in fields such as display technology,integrated circuit technology, etc. In a liquid crystal display (LCD) oran organic light emitting diode (OLED) display, each pixel unit isdriven by a TFT integrated in the pixel unit, so that pictureinformation can be displayed at high speed, high brightness and highcontrast.

Generally, according to the composition of the semiconductor film layerof the TFT, TFTs can be divided into amorphous silicon TFTs,poly-silicon TFTs and oxide TFTs. The electron mobility of poly-siliconTFT can reach 50-200 cm²/V·s, so poly-silicon TFT-LCD has the advantagesof higher resolution, faster reaction speed and higher aperture ratio,etc.

However, because of the orderly lattice arrangement of poly-silicon TFT,the resistance of electrons in it is small, which leads to a largeleakage current in the off state. The excessive leakage current willcause the pixel unit to fail to turn off, thus resulting in poor displayand affecting the normal use of poly-silicon TFT. In order to reduce theleakage current of TFT, the method of modifying TFT structure design(for example, increasing the length of the channel region) can beadopted, the method of lightly doping between source and drain of TFTcan also be adopted, and both of the methods can reduce the leakagecurrent of poly-silicon TFT.

SUMMARY

One embodiment of the present disclosure provides a thin filmtransistor, including: an active layer; a gate insulating layer at oneside of the active layer; a gate electrode at one side of the gateinsulating layer away from the active layer, wherein the gate electrodeincludes an opening, and a part of the active layer overlapped with theopening includes a first lightly doped region, a first heavily dopedregion and a second lightly doped region which are sequentially arrangedin a first direction parallel to a plane where the active layer islocated.

In some examples, in the first direction, parts of the active layerlocated at two sides of the gate electrode and adjacent to the gateelectrode respectively include a third lightly doped region and a fourthlightly doped region, and further includes a second heavily doped regionat one side of the third lightly doped region away from the gateelectrode and a third heavily doped region at one side of the fourthlightly doped region away from the gate electrode, the second heavilydoped region and the third heavily doped region are respectively asource region and a drain region of the thin film transistor.

In some examples, the thin film transistor further includes a sourceelectrode and a drain electrode, respectively electrically connected tothe source region and the drain region.

In some examples, the first lightly doped region, the second lightlydoped region, the third lightly doped region, the fourth lightly dopedregion, the first heavily doped region, the second heavily doped regionand the third heavily doped region have a same doping type.

In some examples, a doping concentration of each of the first heavilydoped region, the second heavily doped region and the third heavilydoped region is 4-25 times a doping concentration of each of the firstlightly doped region, the second lightly doped region, the third lightlydoped region and the fourth lightly doped region.

In some examples, a part of the active layer overlapped with the gateelectrode is a channel region, and a doping type of the channel regionis opposite to the doping type of the first lightly doped region.

In some examples, the channel region includes a first channel region anda second channel region at two sides of the opening in the firstdirection; and in the first direction, the second heavily doped region,the third lightly doped region, the first channel region, the firstlightly doped region, the first heavily doped region, the second lightlydoped region, the second channel region, the fourth lightly doped regionand the third heavily doped region are sequentially connected.

In some examples, the opening includes a first end portion and a secondend portion in a second direction perpendicular to the first direction,the active layer includes a first edge and a second edge in the seconddirection, the first edge is at one side of the active layer close tothe first end portion, the second edge is at one side of the activelayer close to the second end portion, the first edge is aligned withthe first edge or located at an outer side of the first edge, and thesecond end portion is aligned with the second edge or located at anouter side of the second edge.

In some examples, the gate electrode has a stripe shape extending in thesecond direction.

In some examples, the active layer is a low-temperature poly-siliconsemiconductor layer.

One embodiment of the present disclosure further provides an arraysubstrate, including the thin film transistor according to any one ofthe above.

One embodiment of the present disclosure further provides a displaydevice, including the array substrate above-mentioned.

One embodiment of the present disclosure further provides amanufacturing method of a thin film transistor, including: forming anactive layer; forming a gate insulating layer on the active layer;forming a gate electrode on one side of the gate insulating layer awayfrom the active layer, and forming an opening in the gate electrode; andperforming a doping process on the active layer to form a first lightlydoped region, a first heavily doped region and a second lightly dopedregion, which are sequentially arranged in a direction parallel to aplane where the active layer is located, in a part of the active layeroverlapped with the opening.

In some examples, performing a doping process on the active layerincludes: performing a first doping process on the active layer bytaking the gate electrode including the opening as a first mask; andforming a second mask at positions where the first lightly doped regionand the second lightly doped region are formed on the active layer, andperforming a second doping process, wherein a doping concentration ofthe first doping process is lower than a doping concentration of thesecond doping process, so as to form the first lightly doped region, thesecond lightly doped region and the first heavily doped region.

In some examples, upon performing the first doping process on the activelayer by taking the gate electrode including the opening as the firstmask, a third lightly doped region and a fourth lightly doped region arefurther formed, wherein the third lightly doped region and the fourthlightly doped region are respectively at two sides of the gate electrodein the direction and adjacent to the gate electrode; the second mask isalso located at the third lightly doped region and the fourth lightlydoped region, and upon forming the first heavily doped region, a secondheavily doped region is formed at one side of the third lightly dopedregion away from the gate electrode, and a third heavily doped region isformed at one side of the fourth lightly doped region away from the gateelectrode.

In some examples, the method further includes: performing a third dopingprocess on the active layer before the first doping process, wherein adoping type of the third doping process is opposite to doping types ofthe first doping process and the second doping process.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to clearly illustrate the technical solutions of theembodiments of the disclosure, the drawings of the embodiments will bebriefly described in the following; it is obvious that the describeddrawings are only related to some embodiments of the disclosure and thusare not limitative to the disclosure.

FIG. 1 is a schematic structural diagram of a pixel unit including athin film transistor with a U-shaped dual-gate structure;

FIG. 2 is a schematic diagram of the U-shaped dual-gate structure of thethin film transistor illustrated in FIG. 1 ;

FIG. 3 is a schematic diagram of an L-shaped single-gate structure of athin film transistor;

FIG. 4 is a schematic cross-sectional view of the thin film transistorillustrated in FIG. 3 taken along line C-C;

FIG. 5 is a schematic structural diagram of a thin film transistoraccording to an embodiment of the present disclosure;

FIG. 6 is a schematic cross-sectional view of the thin film transistorillustrated in FIG. 5 taken along line D-D;

FIG. 7 is a flowchart of a manufacturing method of a thin filmtransistor according to an embodiment of the present disclosure;

FIGS. 8A-8D are cross-sectional views of processes of a manufacturingmethod of a thin film transistor according to an embodiment of thepresent disclosure; and

FIG. 9 is a flowchart of performing a re-doping process on an activelayer according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

In order to make objects, technical details and advantages of theembodiments of the present disclosure apparent, the technical solutionsof the embodiment will be described in a clearly and fullyunderstandable way in connection with the drawings related to theembodiments of the present disclosure. It is obvious that the describedembodiments are just a part but not all of the embodiments of thepresent disclosure. Based on the described embodiments herein, thoseskilled in the art can obtain other embodiment(s), without any inventivework, which should be within the scope of the present disclosure.

Unless otherwise defined, all the technical and scientific terms usedherein have the same meanings as commonly understood by one of ordinaryskill in the art to which the present disclosure belongs. The terms“first,” “second,” etc., which are used in the description and theclaims of the present application for disclosure, are not intended toindicate any sequence, amount or importance, but distinguish variouscomponents. The terms “comprise,” “comprising,” “include,” “including,”etc., are intended to specify that the elements or the objects statedbefore these terms encompass the elements or the objects and equivalentsthereof listed after these terms, but do not preclude the other elementsor objects. The phrases “connect”, “connected”, etc., are not intendedto define a physical connection or mechanical connection, but mayinclude an electrical connection, directly or indirectly. “Upper”,“lower”, “left”, “right”, etc. are only used to indicate the relativepositional relationship, and when the absolute position of the object tobe described is changed, the relative positional relationship may alsochange accordingly.

In a low-temperature poly-silicon (LTPS) thin film transistor liquidcrystal display or an organic light emitting diode display, when thethin film transistor is used as a control switch of the pixel unit, theU-shaped dual-gate structure is a common design. FIG. 1 is a schematicplane view of a pixel unit including a thin film transistor with aU-shaped dual-gate structure, and FIG. 2 is a schematic plane view ofthe U-shaped dual-gate structure of the thin film transistor illustratedin FIG. 1 . As illustrated in FIG. 1 , the pixel unit includes a gateline 10, a data line 20, a thin film transistor 30 and a pixel electrode40. The thin film transistor 30 is electrically connected to the gateline 10, the data line 20, and the pixel electrode 40, respectively. Thethin film transistor 30 is designed with a U-shaped dual-gate structure.As illustrated in FIG. 2 , the thin film transistor 30 with the U-shapeddual-gate structure includes an active layer and a gate electrode 303.As can be viewed from FIG. 2 , the gate electrode 303 is partiallyoverlapped with the active layer in the direction perpendicular to thesurface of the paper. The active layer is approximately U-shaped andincludes a source region 301, a drain region 302, a channel region 304,a lightly doped region 305 and a heavily doped region 306. The sourceregion 301 and the drain region 302 are respectively located at the twoends of the U-shape. The connection mode of the U-shaped dual-gate thinfilm transistor 30 in the pixel unit is, for example, as illustrated inFIG. 1 . The source region 301 is partially overlapped with the dataline 20 and is connected to the data line 20 through a first via hole50. The drain region 302 is connected to the pixel electrode 40 througha second via hole 60. That is, the thin film transistor directly uses apart of the gate line 10 as the gate electrode 303. This connection modeof the thin film transistor in the pixel unit is conducive to savingspace and improving aperture ratio of the pixel. The part of the activelayer overlapped with the gate electrode 303 is the channel region 304,and the number of the channel regions 304 is two. The active layerlocated at the two sides of each channel region 304 and adjacent to thechannel region includes two lightly doped regions 305, and a heavilydoped region 306 is located at one side of the gate electrode 303 awayfrom the source region 301 and the drain region 302, and each end of theheavily doped regions 306 is respectively connected to one lightly dopedregion 305. For example, the doping concentration and doping type of thesource region 301 and those of the drain region 302 are the same asthose of the heavily doped region 306. The U-shaped dual-gate structureincreases the length of the channel region and adds lightly dopedregions at the two sides of the channel region, thereby effectivelyreducing leakage current.

However, the application of the U-shaped dual-gate TFT is limited bypixels per inch (PPI). For example, in the case where PPI is low, thearea of a single pixel unit is large, and there is enough space for thethin film transistor to have a U-shaped dual-gate structure design asillustrated in FIG. 1 and FIG. 2 . However, for example, in the casewhere PPI is greater than 800, the area of a single pixel unit is small,and the design space of the thin film transistor can no longer allow theuse of the U-shaped dual-gate structure, and only single-gate structurecan be adopted.

FIG. 3 is a schematic diagram of an L-shaped single-gate structure of athin film transistor, and FIG. 4 is a schematic cross-sectional view ofthe thin film transistor illustrated in FIG. 3 taken along line C-C. Asillustrated in FIG. 3 and FIG. 4 , the thin film transistor with theL-shaped single-gate structure includes an active layer, a gateelectrode 303, and a gate insulating layer 307. The gate insulatinglayer 307 is located between the active layer and the gate electrode303. As illustrated in FIG. 3 , the gate electrode 303 is partiallyoverlapped with the active layer in the direction perpendicular to thesurface of the paper. The active layer is L-shaped and includes a sourceregion 301, a drain region 302, a channel region 304 and a lightly dopedregion 305. The source region 301 and the drain region 302 are locatedat the two ends of the active layer, respectively. The part of theactive layer overlapped with the gate electrode 303 is a channel region304. The active layer located at the two sides of the channel region 304and adjacent to the channel region includes two lightly doped regions305.

Compared with the U-shaped dual-gate structure, the L-shaped single-gatestructure reduces the length of the channel region and the number oflightly doped regions, so the leakage current will greatly increase.Therefore, when designing the thin film transistor structure, if theU-shaped dual-gate structure in FIG. 1 is directly replaced with theL-shaped single-gate structure in order to improve the pixels per inch,the leakage current of the thin film transistor will be greatlyincreased, so that the thin film transistor will be difficult to turnoff, and the pixel unit will be in a bright state under the influence ofleakage current, resulting in poor display of products.

Embodiments of the present disclosure provide a thin film transistor, amanufacturing method thereof, an array substrate and a display device.The thin film transistor includes an active layer, a gate insulatinglayer, and a gate electrode. The gate insulating layer is located at oneside of the active layer. The gate electrode is located at one side ofthe gate insulating layer away from the active layer. The gate electrodeincludes an opening, and the part of the active layer overlapped withthe opening includes a first lightly doped region, a first heavily dopedregion and a second lightly doped region which are sequentially arrangedalong a first direction parallel to the plane where the active layer islocated. The thin film transistor can greatly reduce leakage current,and can be used for a display with high pixels per inch.

Hereinafter, the embodiments of the present disclosure will be describedin detail with reference to the accompanying drawings. It should benoted that the same reference numerals in different drawings are used torefer to the same elements already described.

FIG. 5 is a schematic structural diagram of a thin film transistoraccording to an embodiment of the present disclosure, and FIG. 6 is aschematic cross-sectional view of the thin film transistor illustratedin FIG. 5 taken along line D-D. As illustrated in FIG. 5 and FIG. 6 ,the thin film transistor includes an active layer 100, a gate insulatinglayer 200, and a gate electrode 300. The gate insulating layer 200 islocated at one side of the active layer 100 (for example, as illustratedin FIG. 6 , located at the upper side of the active layer 100) andcovers the active layer 100. The gate electrode 300 is located at oneside of the gate insulating layer 200 away from the active layer 100.The gate electrode 300 includes an opening 310, the opening 310penetrates through the gate electrode layer, and the part of the activelayer 100 overlapped with the opening 310 includes a first lightly dopedregion 110, a first heavily doped region 120, and a second lightly dopedregion 130 which are sequentially arranged along the first direction A.For example, the first direction A is a direction parallel to the planewhere the active layer is located. For example, here, the active layerbeing overlapped with the opening means being overlapped in thedirection perpendicular to the active layer (in the thickness directionof the active layer).

In the thin film transistor provided by the present embodiment, theactive layer overlapped with the opening includes a first lightly dopedregion, a first heavily doped region and a second lightly doped regionwhich are sequentially arranged. The first lightly doped region and thesecond lightly doped region can reduce the electric field of the activelayer along the first direction and reduce the hot carriers generated bycollision ionization which is caused by the acceleration of the electricfield, thereby effectively reducing the leakage current. In addition,the overlapping area between the gate electrode and the active layer canbe reduced by setting the opening, so that the parasitic capacitance isreduced, and the anti-crosstalk and anti-flicker levels of the displayusing the thin film transistor are improved.

For example, as illustrated in FIG. 5 and FIG. 6 , the active layer 100further includes a third lightly doped region 140, a fourth lightlydoped region 150, a second heavily doped region 160 and a third heavilydoped region 170. The third lightly doped region 140 and the fourthlightly doped region 150 are parts of the active layer 100 located atthe two sides of the gate electrode 300 and adjacent to the gateelectrode 300, respectively. The second heavily doped region 160 islocated at one side of the third lightly doped region 140 away from thegate electrode 300, the third heavily doped region 170 is located at oneside of the fourth lightly doped region 150 away from the gate electrode300, and the second heavily doped region 160 and the third heavily dopedregion 170 are respectively the source region 160 and the drain region170 of the thin film transistor. The third lightly doped region 140 andthe fourth lightly doped region 150 can further reduce the electricfield of the active layer along the first direction and reduce hotcarriers, thereby further reducing leakage current.

The length (size in the first direction A) and doping concentration ofthe lightly doped region can be designed according to the condition ofthe leakage current. For example, the length of the lightly doped regioncan be adjusted, so that the thin film transistor can achieve the effectof suppressing leakage current without increasing the on-state currentsignificantly, thus not increasing the power consumption of the elementsignificantly. For example, the lengths of the first lightly dopedregion 110, the second lightly doped region 130, the third lightly dopedregion 140 and the fourth lightly doped region 150 are all in the rangeof 0.5 μm to 1.5 μm.

For example, by adjusting the doping concentration of lightly doping,the thin film transistor can achieve the effect of suppressing leakagecurrent without increasing the on-state current significantly, thus notincreasing the power consumption of the element significantly. Forexample, the doping concentrations of the first lightly doped region110, the second lightly doped region 130, the third lightly doped region140 and the fourth lightly doped region 150 are in the range of2×10¹³-5×10¹³ cm⁻³, and the doping concentrations of the first heavilydoped region 120, the second heavily doped region 160 and the thirdheavily doped region 170 are in the range of 2×10¹⁴-5×10¹⁴ cm⁻³.

For example, the doping concentration of each heavily doped region is4-25 times the doping concentration of each lightly doped region.

For example, as illustrated in FIG. 5 and FIG. 6 , the thin filmtransistor further includes an interlayer insulating layer 600, which islocated at one side of the gate electrode 300 away from the active layer100 and covers the gate electrode 300.

For example, as illustrated in FIG. 5 and FIG. 6 , the thin filmtransistor further includes a source electrode 400 and a drain electrode500. A first via hole 410 and a second via hole 510 are provided in theinterlayer insulating layer 600 and the gate insulating layer 200. Thefirst via hole 410 passes through the gate insulating layer 200 and theinterlayer insulating layer 600, so that the source electrode 400 iselectrically connected to the source region 160 through the first viahole 410. The second via hole 510 passes through the gate insulatinglayer 200 and the interlayer insulating layer 600, so that the drainelectrode 500 is electrically connected to the drain region 170 throughthe second via hole 510.

For example, the doping types of the first lightly doped region 110, thesecond lightly doped region 130, the third lightly doped region 140, thefourth lightly doped region 150, the first heavily doped region 120, thesecond heavily doped region 160 and the third heavily doped region 170are the same, and for example, can be N-type doping or P-type doping.

For example, as illustrated in FIG. 5 and FIG. 6 , the part of theactive layer 100 overlapped with the gate electrode 300 is a channelregion 180. For example, the doping type of the channel region 180 isopposite to the doping type of the first lightly doped region 110. Forexample, the doping concentration of the channel region 180 is4×10²²-7×10¹² cm⁻³.

For example, the doping concentration of the lightly doped region isgreater than the doping concentration of the channel region. Forexample, the doping concentration of the lightly doped region can be3-12 times the doping concentration of the channel region. Although thechannel region is slightly doped, the channel region of the active layerstill maintains semiconductor characteristics, thus realizing therelated functions of the thin film transistor.

For example, the first lightly doped region 110, the second lightlydoped region 130, the third lightly doped region 140, the fourth lightlydoped region 150, the first heavily doped region 120, the second heavilydoped region 160 and the third heavily doped region 170 are N-typedoped, and the channel region 180 is P-type doped. However, the presentembodiment is not limited to this case, and the channel region 180 canbe N-type doped, and correspondingly the first lightly doped region 110,the second lightly doped region 130, the third lightly doped region 140,the fourth lightly doped region 150, the first heavily doped region 120,the second heavily doped region 160 and the third heavily doped region170 are P-type doped.

In some examples, as illustrated in FIG. 6 , the channel region 180includes a first channel region 181 and a second channel region 182located at the two sides of the opening 310 along the first direction A.In the first direction A, the second heavily doped region 160, the thirdlightly doped region 140, the first channel region 181, the firstlightly doped region 110, the first heavily doped region 120, the secondlightly doped region 130, the second channel region 182, the fourthlightly doped region 150 and the third heavily doped region 170 aresequentially connected.

The ion doping type of the channel region 180 is opposite to that of thefirst lightly doped region 110, therefore, in the thin film transistorprovided in the above example, four PN junctions are formed in theactive layer 100 along the first direction, and the four PN junctionsare respectively located between the third lightly doped region 140 andthe first channel region 181, between the first channel region 181 andthe first lightly doped region 110, between the second lightly dopedregion 130 and the second channel region 182, and between the secondchannel region 182 and the fourth lightly doped region 150. Because thePN junction has the characteristics of forward turn-on and reverseturn-off, the formed PN junctions can further reduce the leakagecurrent.

In some examples, as illustrated in FIG. 5 , the opening 310 includes afirst end portion 3101 and a second end portion 3102, and the first endportion 3101 and the second end portion 3102 are respectively located atthe two ends of the opening 310 along a second direction B perpendicularto the first direction A. For example, the second direction B is alsoparallel to the plane where the active layer is located. The activelayer 100 includes a first edge 1001 and a second edge 1002, and thefirst edge 1001 and the second edge 1002 are respectively located at thetwo sides of the active layer 100 in the second direction B. The firstend portion 3101 extends beyond the first edge 1001, and the second endportion 3102 extends beyond the second edge 1002. Alternatively, thefirst end portion 3101 is aligned with the first edge 1001, and thesecond end portion 3102 is aligned with the second edge 1002.Alternatively, the first end portion 3101 extends beyond the first edge1001, and the second end portion 3102 is aligned with the second edge1001. Alternatively, the first end portion 3101 is aligned with thefirst edge 1001, and the second end portion 3102 extends beyond thesecond edge 1002. The above four arrangement modes of the opening 310can make the first lightly doped region 110 and the second lightly dopedregion 130 respectively doped to the first edge 1001 and the second edge1002 along the second direction B, which is beneficial to isolate thetwo channel regions 181 and 182 when the thin film transistor is in theoff state, thereby further reducing the leakage current.

For example, as illustrated in FIG. 5 , the gate electrode 300 has astrip shape extending along the second direction B, and the opening 310of the gate electrode also has a strip shape extending along the seconddirection B. In this way, the shape of the gate electrode 300 is similarto a rectangular-ambulatory-plane shape. For example, the strip shape ofthe opening 310 can be a polygon, such as a rectangle, a hexagon, etc.,or can be an approximately oval shape, which is not limited in thepresent disclosure. For example, in the case where the thin filmtransistor is applied to an array substrate, the gate electrode 300 canbe a part of the gate line, and the extending direction of the gateelectrode 300 is the same as that of the gate line; or the gateelectrode 300 is a part protruding from one side edge of the gate line.

In some examples, the active layer 100 is a low-temperature poly-siliconsemiconductor layer, and the thin film transistor is a low-temperaturepoly-silicon thin film transistor.

An embodiment of the present disclosure further provides an arraysubstrate, which includes the thin film transistor provided by any oneof the above embodiments. For example, the array substrate can include,but is not limited to, an array substrate used for a liquid crystaldisplay panel or an array substrate used for an OLED display, and thethin film transistor can be used as a switching transistor or a drivingtransistor. Other elements, such as gate lines, data lines, pixelelectrodes, etc., can be included on the array substrate, and theseelements can be connected to the thin film transistors according to theconnection relationship in related technologies or arranged according tothe positional relationship in related technologies. A single-gatestructure is adopted in the embodiments of the present disclosure,therefore, the area occupied by the thin film transistor can be reduced,thereby further reducing the area of the pixel unit and improving thepixels per inch. Meanwhile, a plurality of lightly doped regions areformed due to the adoption of the gate electrode structure with theopening, and the problem of leakage current of the single-gate structureis alleviated at the same time. Other technical effects of the arraysubstrate are the same as those of the above-mentioned thin filmtransistor, and will not be redundantly described here.

It should be noted that although the L-shaped active layer pattern wasdescribed as an example in the above embodiments, the embodiments of thepresent disclosure are not limited to this case. For example, the activelayer can have an elongated structure extending along the firstdirection A described above. Although the above embodiments have beendescribed taking the top-gate type as an example, the embodiments of thepresent disclosure are not limited to this case. For example, the gateelectrode can also be located under the active layer to form abottom-gate type thin film transistor. Although the source and drainelectrodes are connected to the source and drain regions through viaholes passing through the interlayer insulating layer in the aboveembodiments, the source and drain electrodes can be connected to thesource and drain regions in other ways. For example, the source anddrain electrodes can be formed under the active layer to be directlyconnected to the source and drain regions.

An embodiment of the present disclosure further provides a displaydevice, which includes the array substrate provided by the aboveembodiment. For example, the display device can be implemented as anyproduct or component with display function, such as a liquid crystalpanel, an electronic paper, an organic light emitting diode (OLED)panel, a mobile phone, a tablet computer, a television, a display, anotebook computer, a digital photo frame, a navigator, etc. The displaydevice has the same technical effects as the thin film transistordescribed above, which will not be redundantly described here.

An embodiment of the present disclosure further provides a manufacturingmethod of a thin film transistor. FIG. 7 is a flowchart of themanufacturing method of the thin film transistor, and FIGS. 8A-8D arecross-sectional views of processes of the manufacturing method of thethin film transistor. As illustrated in FIG. 7 and FIGS. 8A-8D, themanufacturing method includes steps S10-S40.

S10, forming an active layer 100, as illustrated in FIG. 8A.

For example, the method of forming the active layer 100 includes:cleaning a base substrate, forming an amorphous silicon film (a-Si) bychemical vapor deposition (CVD), and performing an excimer laserannealing (ELA) process on the amorphous silicon film to convert theamorphous silicon film into a poly-silicon film (p-Si), and patterningthe poly-silicon thin film to form an active layer consisting of aplurality of mutually independent silicon islands. It should be notedthat in FIG. 8A, only one silicon island of the active layer isexemplified, but the active layer 100 includes a plurality of siliconislands, and FIGS. 8B-8D in the following are the same in this aspect.

In some examples, the channel region of the thin film transistor is adoped region. In this case, the method of forming the active layerfurther includes: performing a pre-doping process on the whole region ofthe active layer to form an N-type doped active layer or a P-type dopedactive layer. For example, the pre-doping process can adopt an in-situdoping method, that is, while forming an amorphous silicon film, theamorphous silicon film is doped, then the doped amorphous silicon filmis converted into a poly-silicon film, and the poly-silicon film ispatterned to form an active layer; alternatively, the pre-doping processcan also dope the poly-silicon film after the poly-silicon film isformed; alternatively, the pre-doping process can dope the active layerafter the active layer is formed. For example, the pre-doping process isa lightly doping process. Of course, for the thin film transistor withan undoped channel region, the method of forming the active layer maynot include this step.

S20, forming a gate insulating layer 200 on the active layer 100, asillustrated in FIG. 8B.

For example, the gate insulating layer is formed on the poly-siliconfilm by CVD, and the material of the gate insulating layer is, forexample, SiN_(x).

S30, forming a gate electrode 300 on one side of the gate insulatinglayer 200 away from the active layer 100, and forming an opening 310 inthe gate electrode 300, as illustrated in FIG. 8C.

For example, the gate electrode is formed on the gate insulating layerby using a sputtering process. The material of the gate electrode can bea metal, such as WSi, TaN, MoTa, Cr, Al, etc., or other conductivematerial.

S40: performing a re-doping process on the active layer 100 to form afirst lightly doped region 110, a first heavily doped region 120 and asecond lightly doped region 130, which are sequentially arranged along afirst direction A parallel to the plane where the active layer 100 islocated, as illustrated in FIG. 8D.

For example, for the thin film transistors with a doped channel region,the active layer has been pre-doped. In this case, the doping type ofthe re-doping process is opposite to that of the pre-doping process. Forexample, if the pre-doping is N-type doping, the re-doping is P-typedoping; or, if the pre-doping is P-type doping, the re-doping is N-typedoping.

FIG. 9 is a flow chart of performing a re-doping process on an activelayer. As illustrated in FIG. 9 , in step S40, performing the re-dopingprocess on the active layer includes:

-   -   S401: performing a first doping process on the active layer by        taking the gate electrode including the opening as a first mask;        and    -   S402: forming a second mask at the positions where the first        lightly doped region and the second lightly doped region are        formed on the active layer, and performing a second doping        process on the active layer using the second mask. The first        doping process is a lightly doping process, the second doping        process is a heavily doping process, and the doping        concentration of the first doping process is lower than that of        the second doping process, thereby forming the first lightly        doped region, the second lightly doped region and the first        heavily doped region.

For example, for the thin film transistor with a doped channel region,the active layer has been pre-doped. In this case, the doping types ofthe first doping process and the second doping process are opposite tothe doping type of the pre-doping process, and the doping types of thefirst lightly doped region, the second lightly doped region and thefirst heavily doped region formed by the first doping process and thesecond doping process are opposite to the doping type of the activelayer formed by the pre-doping process. Because the first doping processneeds to neutralize the ions in the active layer after the pre-dopingprocess, it needs a higher ion concentration than the pre-dopingprocess. That is to say, the first doping process firstly needs toreverse the conductivity type of the lightly doped region, and thencontinue doping to form the lightly doped region with the doping typeopposite to that of the channel region. However, this does not mean thatthe doping concentration of the finally formed lightly doped region ishigher than the doping concentration of the channel region. For example,the doping concentration of the lightly doped region can beapproximately equal to the doping concentration of the channel region,and the conductivity types of them can be opposite to each other.

The manufacturing method of the thin film transistor provided by theabove embodiment will be further described below by taking the thin filmtransistor illustrated in FIG. 5 and FIG. 6 as an example.

For the thin film transistor illustrated in FIG. 5 and FIG. 6 , in theabove step S401, the first doping process is performed on the activelayer 100 by taking the gate electrode 300 including the opening 310 asthe first mask, so as to form a third lightly doped region 140 and afourth lightly doped region 150, and the third lightly doped region 140and the fourth lightly doped region 150 are respectively located at thetwo sides of the gate electrode 300 along the first direction A andadjacent to the gate electrode 300.

For the thin film transistors illustrated in FIG. 5 and FIG. 6 , thesecond mask is not only located at the positions corresponding to thefirst lightly doped region 110 and the second lightly doped region 130,but also at the positions corresponding to the third lightly dopedregion 140 and the fourth lightly doped region. In this way, whileforming the first heavily doped region 120, a second heavily dopedregion 160 is formed at one side of the third lightly doped region 140away from the gate electrode 300 along the first direction A, and athird heavily doped region 170 is formed at one side of the fourthlightly doped region 150 away from the gate electrode 300 along thefirst direction A.

For example, the manufacturing method of the thin film transistorprovided by the embodiment of the present disclosure further includes:forming a buffer layer on the base substrate before forming the activelayer; forming an interlayer insulating layer on the gate electrode;forming via holes in the interlayer insulating layer and the gateinsulating layer; forming a source electrode and a drain electrode onthe interlayer insulating layer, wherein the source electrode and thedrain electrode are respectively electrically connected to the secondheavily doped region and the third heavily doped region of the activelayer through the via holes; and other processing steps, which are notredundantly described here.

The manufacturing method of the thin film transistor provided by theembodiment of the present disclosure can be used to manufacture the thinfilm transistor provided by any one of the above embodiments, and hasthe same technical effects as the above thin film transistor, which willnot be redundantly described here.

The following statements should be noted:

-   -   (1) The accompanying drawings involve only the structure(s) in        connection with the embodiment(s) of the present disclosure, and        other structure(s) can be referred to common design(s).    -   (2) In case of no conflict, features in one embodiment or in        different embodiments can be combined.

What have been described above are only specific implementations of thepresent disclosure, the protection scope of the present disclosure isnot limited thereto. Any changes or substitutions easily occur to thoseskilled in the art within the technical scope of the present disclosureshould be covered in the protection scope of the present disclosure.Therefore, the protection scope of the present disclosure should bebased on the protection scope of the claims.

What is claimed is:
 1. A thin film transistor, comprising: an activelayer; a gate insulating layer at one side of the active layer; a gateelectrode at one side of the gate insulating layer away from the activelayer, wherein the gate electrode comprises an opening, and a part ofthe active layer overlapped with the opening comprises a first lightlydoped region, a first heavily doped region and a second lightly dopedregion which are sequentially arranged in a first direction parallel toa plane where the active layer is located, and wherein the openingcomprises a first end portion and a second end portion in a seconddirection perpendicular to the first direction, the active layercomprises a first edge and a second edge in the second direction, thefirst edge is at one side of the active layer close to the first endportion, the second edge is at one side of the active layer close to thesecond end portion, the first end portion is located at an outer side ofthe first edge, and the second end portion is located at an outer sideof the second edge.
 2. The thin film transistor according to claim 1,wherein in the first direction, parts of the active layer located at twosides of the gate electrode and adjacent to the gate electroderespectively comprise a third lightly doped region and a fourth lightlydoped region, and further comprises a second heavily doped region at oneside of the third lightly doped region away from the gate electrode anda third heavily doped region at one side of the fourth lightly dopedregion away from the gate electrode, the second heavily doped region andthe third heavily doped region are respectively a source region and adrain region of the thin film transistor.
 3. The thin film transistoraccording to claim 2, further comprising a source electrode and a drainelectrode, respectively electrically connected to the source region andthe drain region.
 4. The thin film transistor according to claim 2,wherein the first lightly doped region, the second lightly doped region,the third lightly doped region, the fourth lightly doped region, thefirst heavily doped region, the second heavily doped region and thethird heavily doped region have a same doping type.
 5. The thin filmtransistor according to claim 4, wherein a doping concentration of eachof the first heavily doped region, the second heavily doped region andthe third heavily doped region is 4-25 times a doping concentration ofeach of the first lightly doped region, the second lightly doped region,the third lightly doped region and the fourth lightly doped region. 6.The thin film transistor according to claim 4, wherein a part of theactive layer overlapped with the gate electrode is a channel region, anda doping type of the channel region is opposite to the doping type ofthe first lightly doped region.
 7. The thin film transistor according toclaim 6, wherein the channel region comprises a first channel region anda second channel region at two sides of the opening in the firstdirection; and in the first direction, the second heavily doped region,the third lightly doped region, the first channel region, the firstlightly doped region, the first heavily doped region, the second lightlydoped region, the second channel region, the fourth lightly doped regionand the third heavily doped region are sequentially connected.
 8. Thethin film transistor according to claim 1, wherein the gate electrodehas a stripe shape extending in the second direction.
 9. The thin filmtransistor according to claim 1, wherein the active layer is alow-temperature poly-silicon semiconductor layer.
 10. An arraysubstrate, comprising the thin film transistor according to claim
 1. 11.A display device, comprising the array substrate according to claim 10.12. A manufacturing method of a thin film transistor, comprising:forming an active layer; forming a gate insulating layer on the activelayer; forming a gate electrode on one side of the gate insulating layeraway from the active layer, and forming an opening in the gateelectrode; and performing a doping process on the active layer to form afirst lightly doped region, a first heavily doped region and a secondlightly doped region, which are sequentially arranged in a directionparallel to a plane where the active layer is located, in a part of theactive layer overlapped with the opening, wherein the opening comprisesa first tend portion and a second end portion in a second directionperpendicular to the first direction, the active layer comprises a firstedge and a second edge in the second direction, the first edge is at oneside of the active, layer close to the first end portion, the secondedge is at one side of the active layer close to the second end portion,the first edge is aligned with the first edge or located at an outerside of the first edge, and the second end portion is aligned with thesecond edge or located at an outer side of the second edge.
 13. Themethod according to claim 12, wherein performing a doping process on theactive layer comprises: performing a first doping process on the activelayer by taking the gate electrode with the opening as a first mask; andforming a second mask at positions where the first lightly doped regionand the second lightly doped region are formed on the active layer, andperforming a second doping process, wherein a doping concentration ofthe first doping process is lower than a doping concentration of thesecond doping process, so as to form the first lightly doped region, thesecond lightly doped region and the first heavily doped region.
 14. Themethod according to claim 13, wherein upon performing the first dopingprocess on the active layer by taking the gate electrode with theopening as the first mask, a third lightly doped region and a fourthlightly doped region are further formed, wherein the third lightly dopedregion and the fourth lightly doped region are respectively at two sidesof the gate electrode in the direction and adjacent to the gateelectrode; the second mask is also located at the third lightly dopedregion and the fourth lightly doped region, and upon forming the firstheavily doped region, a second heavily doped region is formed at oneside of the third lightly doped region away from the gate electrode, anda third heavily doped region is formed at one side of the fourth lightlydoped region away from the gate electrode.
 15. The method according toclaim 13, further comprising: performing a third doping process on theactive layer before the first doping process, wherein a doping type ofthe third doping process is opposite to doping types of the first dopingprocess and the second doping process.